This invention relates to an image pickup system for use in combination with a craft, such as a spacecraft, flying over an object zone which is typically on the ground surface of the earth. Such an image pickup system is particularly useful in a remote sensing system for the earth.
An image pickup system of the type described is used to remotely sense an object zone on board a craft flying over an object zone along a flying direction at a predetermined flight altitude. In a remote sensing system, it is often necessary to pick up a stereo image, such as a stereo topographic image, from the object zone by the use of the image pickup system. In order to provide the stereo image, the object zone should be picked up, along the flying direction at two positions spaced apart from each other, so as to form two optical images of the object zone. A conventional image pickup system has at least two optical systems for deriving the stereo image. Such a conventional image pickup system has a disadvantage such that it inevitably becomes heavy and bulky.
In order to remove the above-described disadvantage, an improved image pickup system is disclosed in U.S. Pat. No. 4,613,899 issued to Ryushi Kuwano et al and assigned to the instant assignee. In the image pickup system of the Kuwano et al patent, a single optical system is used in the craft to form, on a focussing area, optical images of forward and backward zones lying transversely of the flying direction in the object zone. The forward and the backward zones are positioned at a predetermined distance along the flying direction. Forward and backward optical images are picked up from the forward and the backward zones. The forward and the backward optical images are transduced into forward and backward electrical signals by the use of forward and backward photoelectric transducing members, respectively, placed on the focussing area with a gap left therebetween. The forward and the backward electrical signals are processed so that the forward and the backward optical images are reproduced either on board the craft or in a ground station to provide the stereo image. In practice, the forward electrical signal is delayed by a predetermined time interval into a delayed signal. The predetermined time interval is such that the delayed electrical signal appears concurrently with the backward electrical signal. In other words, the delayed signal is produced after the craft flies the predetermined distance.
The ratio between the flight altitude of the craft and the predetermined distance is called a base height ratio in the art. If the object zone has hills and valleys, it is desirable that the base height ratio should have a small value in order to clearly represent the hills and the valleys. If the object zone is flat, the base height ratio should have a large value.
The stereo image pickup system of the Kuwano et al patent provides a single base height ratio alone and therefore can not provide the stereo images with various base height ratios.